Such a spindle is, for example, known from EP 14 09 197 B1 in which a tie rod loaded at one side by a spring package is arranged in a continuous bore, said tie rod comprising at its one end a clamping head with which the tool can be retracted in a clamping cone of said tool spindle. In order to supply the tools with lubricating or cooling means, the tie rod itself comprises a longitudinal bore to which a non-rotating conduit is coupled via a rotational bushing. The work piece spindle is rotationally bearing-mounted in the direction of the rotating axis in front of and behind the driving motor consisting of a rotor and a stator. A clamping cylinder is flange-mounted to said spindle case which is able to push the tie rod against the spring force in order to release the tool tension. The rotational bushing is arranged in the zone of the rear rolling bearing.
Another tool spindle is known from EP 17 87 744 A1 having a similar construction as that described above. In this spindle the rotational bushing is arranged in the zone of the ring cylinder.
Both embodiments have the disadvantage that their construction length is relatively long and, therefore, they need some space in the working space of turning and milling machines. Further, the danger of collisions with surrounding parts or other aggregates of the machine increases, especially in machine tools having a pivotable spindle unit.
EP 2 554 301 A1 shows a generic working spindle in which the releasing unit for the tool is integrated into the spindle.
EP 2 138 253 A1 shows a motor spindle comprising a conventional construction and a sensor provided outside of the working spindle for detecting the position of the tie rod of the releasing unit.
Further, motor spindles are known from the prior art in which the clamping cylinder is integrated into the spindle shaft and, therefore, also rotates. In this manner, when changing the tool, the power flow may completely be introduced into the shaft, such that special means for releasing the rolling bearings may be omitted. An example of such a spindle is described in the article “Wellenkühlung optimiert Motorspindeln”, Schweizer Maschinenmarkt 19, 2011, pages 114 to 117. However, such clamping cylinders which are integrated into the shaft present complexly configured rotational bushings which have to transfer three fluids in order to introduce the cooling agent and to introduce the hydraulic driving.